UV replication technology may be used for producing and/or replicating optical and mechanical structures.
In this technology, a UV-curing plastic or polymer, for example Ormocere, UV adhesives by Delo, Norland, Epoxy Technology, Panacol-Elosol, is molded into the desired shape by using a molding tool, and is cured by means of UV radiation, for example. Molding is effected in a mask aligner enabling exact positioning of the molding tool with regard to marks on the substrate on which the molding is to be effected. To perform the curing, the entire surface area of the polymer present on the substrate is irradiated simultaneously with UV radiation through the tool or the substrate and thus is cured.
Since curing is performed in all positions at the same time, the inevitable shrinking will lead to stresses building up which, once the tool has been removed, will be result in shape deviations of the molded structures and in bending of the substrate. If the substrates provided with polymeric structures are to be connected to further substrates, this will result in tolerance-related and procedural problems, such as in the integration of camera objectives at the wafer level.
By way of example, FIG. 19 shows, on the left-hand side, the polymer shrinkage resulting from the UV irradiation and, thus, the shape deviation between the tool and the structure molded, which cannot be accepted specifically for optical applications. The right-hand side of FIG. 19 further shows that in addition to the shape deviation, the polymer shrinkage also leads to tensile stress and a bending of the substrate on which the polymer has been molded.
The publication /1/Jiseok LIM, Minseok CHO, Hokwan KIM, and Shinil KANG: “Fabrication of Hybrid Microoptics Using UV Imprinting Process with Shrinkage Compensation Method”, Japanese Journal of Applied Physics, Vol. 47, No. 8, 2008, pp. 6719-6722, shows an adjustable aperture (aperture) for shrinkage compensation in producing hybrid lenses, which represent a combination of spherical glass lenses with an additional polymer film for producing an aspherical profile. The UV irradiation of the polymer is effected through the lens substrate. Variable iris lenses are proposed as aperture layers in this document; however such iris lenses are mechanically complicated and, thus, expensive and have increased installation space requirements.